Ask The Experts
Solid Fuel Appliances

I have a fireplace in my house that has cinder block
walls and a slate floor area (where the fire burns). Both of these areas
are covered with burn residue and I was wondering if you could give me
some guidance as to what to use to clean the fireplace walls and floor.

Creosote and other residue that has been burned into masonry surfaces
can be extremely difficult to remove. After scraping off any mechanically
removable material, we would recommend the use of over-the-counter glass
and hearth cleaners, which should be available at any store specializing
in stove and fireplace sales and installations. The chemicals are quite
potent and should only be used following the manufacturer’s directions,
including wearing appropriate safety protection. Making the surfaces
look like new will be out of the question, but the worst of it can probably
be cleaned up.

We are concerned about the description of your fireplace. Neither slate
nor cinder block are appropriate materials for the hearth and firebox
portion of your fireplace. Extreme heat can cause the slate to crack
violently, and will likely cause significant deterioration of the block.
These surfaces should be constructed with firebrick and mortar designed
for high heat. Masonry fireplaces that are amateurishly built, or do
not meet the highest standards may pose a serious fire hazard. We recommend
that you have the fireplace thoroughly evaluated.

There are many signs of poor workmanship. Some of the common defects
that we see include projecting trim wood too close to the face of the
firebox opening, (minimum 6 inches on the sides and 12 inches above),
inadequate extension of the hearth in front of the fireplace, (16 inch
minimum), wood forms remaining below the hearth or hearth extension,
missing clay tile flue liners in the chimney, gaps between flue liner
sections, cracked or broken liners, rusted out dampers, gaps between
the masonry fireplace front and the firebox, and loose or deteriorated
firebricks. Unfortunately, some defects can remain hidden, but a thorough
inspection may reveal defects that should bring into question the safety
of the entire fireplace system. Sometimes the best approach may be to
clean up and seal the fireplace and convert it into a decorative element.

I often get a smoky smell coming from my fireplace
in the family room, even when it isn't in use. What can I do to stop
this?

A smoky odor from an unused fireplace is a sure sign of negative air
pressure. Warm air naturally rises, creating a slight vacuum or negative
pressure in the lower parts of the house, drawing replacement air in
from the exterior. In a tight house, this may mean drawing the air down
the chimney where it picks up smoke odors. Fireplaces in the basement
commonly have this problem. The first step is to make sure that the
chimney damper, just above the firebox, is tightly sealed. If it can’t
be sealed, replace it. Then make sure that the fireplace doors seal
well. Steps to reduce the negative pressure in the house may also help.
In addition to the natural rise of warmed air, all of our ventilating
devices pull air out of the house, requiring exterior air to replace
the vented air. Cracking a window open on the lower level may be helpful
when running ventilators.

While a mild smoke odor is a minor problem, the issue can be very serious
if the same thing occurs with naturally drafting gas appliances. The
same negative pressure could be drawing combustion gases including carbon
monoxide back down the utility chimney, posing a very unhealthy situation.
If this problem is a possibility in your house, make sure your carbon
monoxide detector is in good working order, and call in a professional
for further assessment.

I have an older house with a masonry fireplace. I
have been told that the flue is unlined, and that I shouldn't use the
fireplace. While I sometimes have a problem, especially on windy days,
with occasional smoke in the house, the fireplace has worked fine. Is
relining the chimney critical? It’s very expensive.

The vast majority of masonry fireplace chimneys have a clay tile liner.
The liner is a very durable clay cylinder designed to endure the stresses
of temperature and moisture that flues are exposed to as smoke and water
vapor escape from the fireplace. Without a liner the less durable bricks
and mortar are exposed to these stresses and will deteriorate. Crumbling
mortar and brick could clog the flue. In addition, the added line of
defense provided by the liner is critical to protect the house in case
of a chimney fire. Not only is a liner necessary, the integrity of the
liner is also critical. Any cracks in the liner could cause the liner
to fail during a chimney fire. It is certainly possible that with light
use, you can get away without the liner, but you are putting your home
and family at risk.

Modern fireplace, woodstove, and chimney design is moving away from
masonry and clay tile liners. Masonry does not work as well as the insulated
metal chimneys and woodstoves commonly installed today. Older systems
were not designed with efficiency in mind. Modern efficient units have
lower stack temperatures, resulting in poor draft in cold masonry chimneys.

The smoke entry problem that you occasionally experience is probably
due to improper design. There are many potential design flaws that could
lead to this condition, but by far the most common is that the chimney
is not tall enough. The rule of thumb is that the top of the chimney
should be a minimum of 2 foot above any portion of roof that comes within
10 foot of the chimney. This is usually roughly discernable by looking
from the ground at the nearby roof. A steeper roof requires a taller
chimney.

Whatever fireplace or chimney design you have, it is necessary to have
the unit regularly inspected and the flue cleaned to prevent the creosote
build-up that could result in a dangerous chimney fire.

I have a five-year-old fireplace in my living room.
When it rains heavily I hear a dripping sound but can’t find any leakage.
Should I be concerned?

Keeping rainwater out of fireplaces is important, whatever type of fireplace
you may have. Chronic moisture can cause very expensive damage and render
the fireplace unsafe or unusable. With traditional masonry fireplaces
prevention is often no more difficult than adding a rain cap above the
open flue at the top of the chimney. Metal rain caps that mount on the
top of the clay tile flue of the chimney not only keep rain out, but
act as a spark arrester and help keep critters out. In your case though,
we suspect that you have a zero-clearance type fireplace. This is a
metal fireplace unit that mounts into a wood framed chaseway. Most new
fireplaces are of this type. The metal chimney and chimney cap are an
integral part of the entire assembly, as provided by the manufacturer,
and should be installed as directed. Zero-clearance fireplaces should
not be mixed and matched with other products or built into masonry chimneys.
Check to make sure that you see a metal cap at the top of the chimney
flue. But, the more likely leakage point in your case is the roof on
the top of the chaseway itself. This is generally field built and is
often inadequate, especially if the top of the chimney chaseway is flat.
The only sure way to provide a watertight top to a flat chimney chase
is by installing a soldered metal type covering. The metal top should
have one or more “boots” to allow passage of the fireplace flue and any
other flue that might use the same chaseway, and a separate ring or rings
called collars which tighten fast around each flue to shed water away
from the “boot”. Caulking the “boots” is simply not reliable and will
soon result in leakage. Not only will damage occur to the zero-clearance
fireplace, but we have often seen massive damage to the wood framing
and sheathing that surrounds the fireplace unit. The dripping that you
hear is probably water landing out of view on the top of the metal fireplace
unit. The problem though will most likely need to be solved at the top
of the chimney.

I often get a smoky smell coming from my fireplace
in the family room, even when it isn't in use. What can I do to stop
this?

A smoky odor from an unused fireplace is a sure sign of negative air
pressure. Warm air naturally rises, creating a slight vacuum or negative
pressure in the lower parts of the house, drawing replacement air in
from the exterior. In a tight house, this may mean drawing the air down
the chimney where it picks up smoke odors. Fireplaces in the basement
commonly have this problem. The first step is to make sure that the
chimney damper, just above the firebox, is tightly sealed. If it can’t
be sealed, replace it. Then make sure that the fireplace doors seal
well. Steps to reduce the negative pressure in the house may also help.
In addition to the natural rise of warmed air, all of our ventilating
devices pull air out of the house, requiring exterior air to replace
the vented air. Cracking a window open on the lower level may be helpful
when running ventilators.

While a mild smoke odor is a minor problem, the issue can be very serious
if the same thing occurs with naturally drafting gas appliances. The
same negative pressure could be drawing combustion gases including carbon
monoxide back down the utility chimney, posing a very unhealthy situation.
If this problem is a possibility in your house, make sure your carbon
monoxide detector is in good working order, and call in a professional
for further assessment.

I have large masonry fireplace in the living room that
often puffs smoke back into the room when I use it. The damper is open
and the chimney is clean. What can I do to make it work better?

There are a lot of potential causes for the drafting problem that you
are experiencing with your fireplace. The smoke should readily draft
up the chimney because warm air rises, but a lot of other factors may
be preventing an adequate flow. These include a fireplace opening that
is too large for the flue size, an overly cold flue on an exterior wall,
a poorly configured smoke shelf above the firebox, and a damper that
won’t fully open. But, the most common cause is a chimney that is too
short. A taller chimney will contain more warm air, creating a greater
updraft. Often, the chimney is not sufficiently tall in relation to
the adjacent roof, resulting in a downflow of air at the top of the chimney
as the wind moves over the peak of the roof toward the chimney. By code
the chimney should be a minimum of 2 foot taller than any portion of
roof within 10 foot of the chimney. Extending the height of the chimney
is a common solution for this problem. Every chimney should have a rain
cap over the flue. If all else fails it may be helpful to install a
baffle between the flue and the cap on the uphill side of the chimney
to deflect the wind coming over the roof.

Another common problem is a house that is too tight. Most homes operate
under negative pressure. This means that there is more air leaving the
house via chimneys, ventilators, dryer exhausts, etc. than is entering
the house, through cracks and gaps in the exterior and interior finishes.
If opening a window makes the fireplace draft better, it’s time to add
an exterior air source. Since 1980, the NYS Energy Code has required
that a ducted exterior air source be installed in the front of a fireplace.
In most instances this can be retrofitted to an existing fireplace.
An exterior air source will not only make the fireplace draft better,
but will also save you money. Tremendous heat losses occur as the fireplace
pulls the interior air that your furnace has labored to keep warm right
up the chimney. Using exterior air to feed the fireplace can cut down
on these losses, especially if glass doors are used to restrict the amount
of heated interior air entering the fireplace.